The present invention relates to a method of dynamically changing the formation of addresses in the memory of a data processing system.
Owing to the recent, remarkable development of hardware technology, it is possible now to use memories of greater capacity in data processing systems, and demand for such memories is growing acceleratedly stronger in the market, too. When increasing the capacity of the memory of a data processing system, however, the capability to address the memory needs to be augmented also, which necessitates an alternation of visibility to the software. As a result, it becomes impossible to use programs, adapted for conventional data processing systems, in expanded data processing systems having capabilities to address memories of large capacities, and the consequence is grave.
For the purpose of obviating this problem in a data processing system capable of changing the address formation, a method has been heretofore proposed which gives the hardware a new function in addition to the usual one for execution of existing programs and determines which funciton to use at the time of raising the system. U.S. patent application No. 265,122/1981 (Japanese Preliminary Patent Publication No. 57-3284) discloses an address control system wherein the address field of an instruction is divided into a first field and a second field having a displacement address indicative of a displacement from the base address, and the addressing capability is expanded by adding to the displacement address the relocation addresses of the index and segment designated by the first field. According to this method, once the system is raised, only the program corresponding to the prescribed function can be used. But, on account of the structure of programs, it is common that a newly developed program uses the existing original program as a subroutine. It is, therefore, a serious disadvantage that a program developed corresponding to a new function can not use as a subroutine the program which can be executed solely in the existing original function.